common: change conflicting makefile variable

Because tests and examples are now compiled and linked using both c
and c++ compilers a special makefile variable was required to identify
the language. It was named LANG - unfortunately that conflicts with
locale settings, the new name is COMPILE_LANG.

src/examples/Makefile.inc

@@ -47,7 +47,7 @@ LDFLAGS = -Wl,-rpath=$(LIBDIR) -L$(LIBDIR) $(EXTRA_LDFLAGS)
 INCS = -I$(INCDIR) -I.
 
 LINKER=$(CC)
-ifeq ($(LANG), cpp)
+ifeq ($(COMPILE_LANG), cpp)
 LINKER=$(CXX)
 endif
 

src/examples/libpmemobj/cpp/Makefile

@@ -33,7 +33,7 @@ PROGS = queue
 
 LIBS = -lpmemobj -lpmem -pthread
 
-LANG = cpp
+COMPILE_LANG = cpp
 include ../../Makefile.inc
 
 queue: queue.o

src/test/Makefile.inc

@@ -128,7 +128,7 @@ CFLAGS += $(COMMON_FLAGS)
 LDFLAGS = -Wl,--warn-common -Wl,--fatal-warnings $(EXTRA_LDFLAGS)
 
 LINKER=$(CC)
-ifeq ($(LANG), cpp)
+ifeq ($(COMPILE_LANG), cpp)
 LINKER=$(CXX)
 endif
 

src/test/obj_cpp_ptr/Makefile

@@ -35,7 +35,7 @@
 #
 TARGET = obj_cpp_ptr
 OBJS = obj_cpp_ptr.o
-LANG = cpp
+COMPILE_LANG = cpp
 
 LIBPMEM=y
 LIBPMEMOBJ=y